Organic light emitting devices

ABSTRACT

An organic light emitting device has a layer structure comprising: a first electrode layer ( 20 ); a second electrode layer ( 40 ) parallel to the first electrode layer ( 20 ); and, an electrically conductive and light transmissive layer ( 70 ) parallel to the second electrode layer. An electrically insulating layer ( 30 ) is disposed between the first and second electrode layers. A layer of organic material ( 50 ) is disposed between the second electrode layer and the conductive layer. An aperture ( 60 ) in the organic layer provides an electrical connection path between the conductive layer and one of the first and second electrode layers.

FIELD OF INVENTION

[0001] The present invention relates to organic light emitting devicesfor display applications and to methods for fabricating such devices.

BACKGROUND

[0002] Organic light-emitting devices (OLEDs) are typically manufacturedas a sequence of layers deposited on top of each other to form a layerstructure. The layer structure typically comprises a first electrode ona supporting substrate and several organic layers disposed between thefirst electrode and a second electrode. Light output is generated bycharge injection into the organic material via the electrodes. Theorganic material emits photons on excitation by the injected charge. Atleast one of the electrodes is typically formed from a lighttransmissive material such as Indium Tin Oxide (ITO) or a thin metal topermit passage of light out of the device.

SUMMARY OF THE INVENTION

[0003] In accordance with the present invention, there is now providedan organic light emitting device having a layer structure comprising: afirst electrode layer; a second electrode layer parallel to the firstelectrode layer; an electrically conductive and light transmissive layerparallel to the second electrode layer; an electrically insulating layerdisposed between the first and second electrode layers; a layer oforganic material disposed between the second electrode layer and theconductive layer; an aperture in the organic layer providing anelectrical connection path between the conductive layer and one of thefirst and second electrode layers.

[0004] Preferably, the first electrode layer, the second electrodelayer, the insulating layer, and the conductive layer each comprise anarray of parallel strips, the strip of the first electrode layerextending orthogonal to the strips of the second electrode layer. Thestrips of the insulating layer and the conductive layer may extendorthogonal to the strips of the first electrode layer. Alternatively,the strips of the insulating layer and the conductive layer may extendorthogonal to the strips of the second electrode layer.

[0005] In preferred embodiments of the present invention, there isprovided a plurality of apertures in the organic layer eachcommunicating with one of the first and second electrode layers. Eachaperture may be located at a different intersection of a strip of thefirst electrode layer and a strip of the second electrode layer. Eachaperture may extend in a direction parallel to the strips of the secondelectrode layer. Alternatively, each aperture may extend in a directionparallel to the strips of the first electrode layer.

[0006] The strips of the conductive layer may be electrically connectedto corresponding strips of the second electrode layer. Alternatively,the strips of the conductive layer may be electrically connected tocorresponding strips of the first electrode layer.

[0007] Viewing the present invention from another aspect, there is nowprovided a method for fabricating an organic light emitting device, themethod comprising: depositing a first electrode layer on a substrate;depositing an electrically insulating layer on the first electrodelayer; depositing a second electrode layer on the insulating layer;depositing an organic layer on the second electrode layer; forming anaperture in the organic layer; depositing a light transmissiveelectrically conductive layer on the organic layer; and forming anelectrical connection between the conductive layer and one of the firstand second electrode layers via the aperture.

[0008] In a preferred embodiment of the present invention to bedescribed shortly, there is provided a passive matrix OLED comprising asubstrate on which is disposed a first electrode layer comprising anarray of parallel strips. An insulating layer is disposed on the firstelectrode layer. The insulating layer also comprises an array ofparallel strips. The strips of the insulating layer extend in adirection which is orthogonal to the strips of the first electrodelayer. A second electrode layer is disposed on the insulating layer. Thesecond electrode layer also comprises an array of parallel stripsrunning orthogonal to the strips of the first electrode layer. Thestrips of the second electrode layer overlay the insulating layer. Thefirst electrode layer is thus electrically isolated from the secondelectrode layer by the insulating layer. An layer of organic material isdisposed on the second electrode layer. The organic layer extendshomogeneously across the strips of the second electrode layer, the firstelectrode layer, and the intervening insulating layer. Apertures areformed in the organic layer. The apertures communicate with theunderlying second electrode layer. The organic layer is covered with alight transmissive, electrically conductive layer. Electrical contactsbetween the strips of the second electrode layer and the conductinglayer are formed via the apertures in the organic layer. The conductinglayer comprises an array of parallel strips running parallel to thestrips of the second electrode layer. A partition runs between adjacentstrips of the conductive layer. The OLED is thus divided into a matrixof addressable light emitting picture elements.

[0009] OLEDs embodying the present invention are advantageous in thatthe first and second electrodes need not be fabricated from atransparent conductor such as Indium Tin Oxide. Instead, the first andsecond electrode may be selected from a broader range of materials. Theelectrical characteristics of the first and second electrodes can thusbe optimized in the interests of, for example, improving luminousefficiency and reducing potential drops across the display area. Suchpotential drops would otherwise impair the quality of the displayedimage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Preferred embodiments of the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings, in which:

[0011]FIG. 1 is a plan view of a substrate with a first electrode layerdisposed thereon;

[0012]FIG. 2 is a cross-sectional view of the substrate of FIG. 1 in theplane A-A′ when viewed in the direction of the arrows,

[0013]FIG. 3 is a plan view of the substrate with an insulating layerdisposed on the first electrode;

[0014]FIG. 4 is a cross-sectional view of the substrate of FIG. 3 in theplane A-A′ when viewed in the direction of the arrows;

[0015]FIG. 5 is a plan view of the substrate with a second electrodelayer disposed on the insulating layer;

[0016]FIG. 6 is a cross-sectional view of the substrate of FIG. 5 in theplane A-A′ when viewed in the direction of the arrows;

[0017]FIG. 7 is a plan view of the substrate with an organic layerdisposed on the insulating layer;

[0018]FIG. 8 is a cross-sectional view of the substrate of FIG. 7 in theplane A-A′ when viewed in the direction of the arrows;

[0019]FIG. 9 is a plan view of the substrate with apertures formed inthe organic layer;

[0020]FIG. 10 is a cross-sectional view of the substrate of FIG. 9 inthe plane A-A′ when viewed in the direction of the arrows;

[0021]FIG. 11 is a plan view of the substrate with an electricallyconducting layer disposed on the organic layer;

[0022]FIG. 12 is a cross-sectional view of the substrate of FIG. 11 inthe plane A-A′ when viewed in the direction of the arrows;

[0023]FIG. 13 is a plan view of the substrate with the conducting layershaped to provide discrete emission areas;

[0024]FIG. 14 is a cross-sectional view of the substrate of FIG. 13 inthe plane B-B′ when viewed in the direction of the arrows;

[0025]FIG. 15 is a modification of the plan view of FIG. 14 showing thedisplay areas;

[0026]FIG. 16 is a is a plan view of another example of an OLEDembodying the present invention; and,

[0027]FIG. 17 is a cross-sectional view of the OLED of FIG. 13 in theplane C-C′ when viewed in the direction of the arrows;

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0028] What follows now is a description of a passive matrix OLEDembodying the present invention and methods for fabricating such anOLED.

[0029] Referring first to FIGS. 1 and 2 in combination, in a preferredembodiment of the present invention, first electrode layer ofelectrically conducting material 20 is deposited on a substrate 10. Thesubstrate 10 may be formed from a light transmissive material such asglass or plastics or from an opaque material such as a Silicon wafer.The first electrode layer 20 may be formed from a range of differentmaterials, including but not limited to Indium Tin Oxide, Indium ZincOxide, Aluminum Zinc Oxide, Aluminum, Nickel, Copper, Platinum, andIridium, or combinations of the aforementioned materials with organicand/or inorganic charge injection layers. The first electrode layer 20comprises an array of parallel strips. In particularly preferredembodiments of the present invention, the strips of the first electrodelayer 20 can be formed by evaporation and liftoff processes. The liftoffprocess typically involves applying a pattern of photo-resist to thesubstrate 10 prior to evaporation of the first electrode layer 20 ontothe substrate 10 and then removing the portions of the first electrodelayer 20 overlying the resist pattern. The evaporation process may bereplaced by sputtering or electroless plating. The liftoff process maybe replaced by wet or dry etching.

[0030] With reference now to FIGS. 3 and 4 in combination, an insulatinglayer 30 is then deposited on the first electrode layer 20. Theinsulating layer 30 may be formed from a range of materials includingphoto-resists, polymers, organic and inorganic insulators, Siliconoxide, Silicon Nitride, Tantalum Oxide, together with other Oxides,Nitrides, and Fluorides. The insulating layer 30 also comprises an arrayof parallel strips. The strips of the insulating layer 30 extend in adirection which is orthogonal to the strips of the first electrode layer20. In particularly preferred embodiments of the present invention, thestrips of the insulating layer 30 are formed by deposition and liftoffprocesses. Wet or dry etching may be employed by way of alternative tothe liftoff process.

[0031] Turning now to FIGS. 5 and 6 in combination, a second electrodelayer 40 is then deposited on the insulating layer 30. The secondelectrode layer 40 may be formed from a range different materials,including but not limited to transparent organic conductors, Indium TinOxide, Indium Zinc Oxide, Aluminum Zinc Oxide, Aluminum, Nickel, Copper,and Platinum-Iridium. The second electrode layer 40 also comprises anarray of parallel strips running orthogonal to the strips of the firstelectrode layer 20. The strips of the second electrode layer 40 overlaythe strips of the insulating layer 30. The first electrode layer 20 isthus electrically isolated from the second electrode layer 40 by theinsulating layer 30. In particularly preferred embodiments of thepresent invention, the strips of the second electrode layer 40 may beformed by the aforementioned evaporation, sputtering, electrolessplating, liftoff, wet etch and dry etch processes, or combinationsthereof

[0032] Referring now to FIGS. 7 and 8 in combination, a layer of organicmaterial 50 is then deposited on the second electrode layer 40. Theorganic layer 50 comprises active components which are emissive of lightwhen electrically stimulated. These active components may be relativelysmall organic molecules or organic polymers such as a poly(phenylenevinylene). The organic layer 50 extends homogeneously across the stripsof the second electrode layer 40, the first electrode layer 20, and theintervening insulating layer 30. The organic layer 50 may comprise asingle layer of organic material. However, in particularly preferredembodiments of the present invention, the organic layer 50 comprises acomposite organic layer including a stack of organic layers. Inpreferred embodiments of the present invention, the organic layer 50 isdeposited on the second electrode layer 40 by thermal evaporation.

[0033] With reference to FIGS. 9 and 10 in combination, apertures 60 arethen formed in the organic layer 50 at each intersection of the stripsof the first electrode layer 20 and the strips of the second electrodelayer 40. The apertures 60 communicate with the underlying secondelectrode layer 40.

[0034] Referring now to FIGS. 11 and 12 in combination, the organiclayer 50 is then covered with a light transmissive, electricallyconductive layer 70. The conductive layer 70 may be formed from a rangeof materials, including but not limited to organic conductors such aspolyaniline, polythiophene and derivatives thereof, and Indium Tin Oxideand semi transparent metals, for example. Electrical contacts betweenthe strips of the second electrode layer 40 and the conductive layer 70are formed via the apertures 60 in the organic layer 50.

[0035] With reference to FIGS. 13 and 14 in combination, the conductivelayer 70 is partitioned into parallel strips each connected to theunderlying strip of the second electrode layer 40. A partition 80 runsbetween adjacent strips of the conductive layer 80. The OLED is thusdivided into a matrix of addressable light emitting picture elements 90.

[0036] In particularly preferred embodiments of the present invention,the apertures 60 are formed by localized laser ablation of the organiclayer 50. In particularly preferred embodiments of the presentinvention, the conductive layer 70 is deposited on the organic layer 50by evaporation. The conductive layer 70 is then partitioned into stripsby laser ablation. Alternatively, the apertures 60 may be formed byapplying stripes of photo-resist having negative edges to the secondelectrode layer 40 and then depositing the organic layer 50 andconductive layer 70 using different evaporation angles. Such shadowingeffects, together with dry liftoff or stamping may also be employed topartition the conductive layer 70. Stamping may also be used to createthe apertures 60.

[0037] Remaining with FIGS. 14 and 15, a preferred example of an OLEDembodying the present invention comprises a substrate 10 on which isdisposed a first electrode layer 20 comprising an array of parallelstrips.

[0038] An insulating layer 30 is disposed on the first electrode layer.The first electrode layer 20 is thus disposed between the substrate 10and the insulating layer 30. The insulating layer 30 also comprises anarray of parallel strips. The strips of the insulating layer 30 extendin a direction which is orthogonal to the strips of the first electrodelayer 20.

[0039] A second electrode layer 40 is disposed on the insulating layer30. The insulating layer 30 is thus disposed between the first electrodelayer 20 and the second electrode layer 40. The second electrode layer30 also comprises an array of parallel strips running orthogonal to thestrips of the first electrode layer 20. The strips of the secondelectrode layer 40 overlay the insulating layer 30. The first electrodelayer 20 is thus electrically isolated from the second electrode layer40 by the insulating layer 30.

[0040] A layer of organic material 50 is disposed on the secondelectrode layer 40. The second electrode layer 40 is thus disposedbetween the organic layer 50 and the insulting layer 30. The organiclayer 50 extends homogeneously across the strips of the second electrodelayer 40, the strips of the first electrode layer 20, and theintervening insulating layer 30.

[0041] Apertures 60 are provided in the organic layer 50 at eachintersection of the strips of the first electrode layer 20 and thestrips of the second electrode layer 40. The apertures 60 communicatewith the underlying second electrode layer 40. The organic layer 50 iscovered with an electrically conductive layer 70. The organic layer 50is thus disposed between the conductive layer 70 and the secondelectrode layer 40. Electrical contacts between the strips of the secondelectrode layer 40 and the conducting layer 70 are formed via theapertures 60 in the organic layer 50. The conducting layer 70 comprisesan array parallel strips running parallel to the strips of the firstelectrode layer 20. A partition 80 runs between adjacent strips of theconductive layer 80. The OLED is thus divided into a matrix of lightemitting picture elements 90.

[0042] Each element 90 corresponds to a different intersection of thestrips of the first electrode layer 20 and the strips of the secondelectrode layer 40. Thus, each element 90 can be addressed via adifferent combination of a strip of the first electrode layer 20 and astrip of the second electrode layer 40. Each element 90 is stimulated toemit light by applying a potential difference between the correspondingstrip of the first electrode layer 20 and the corresponding strip of thesecond layer 40. One of the first and second electrode layers serves asan anode while the other serves as a cathode depending of the directionof application of the potential difference.

[0043] Referring now to FIGS. 16 and 17 in combination, in amodification of the OLED hereinbefore described with reference to FIG.14, the apertures 60 communicate between the conductive layer 70 and thefirst electrode layer 20 through the organic layer 50. The firstelectrode layer is again partitioned into strips. Electrical contactsbetween the strips of the first electrode layer 20 and the conductinglayer 70 are formed via the apertures 60. However, the strips of theconductive layer 70 now run parallel to the strips of the firstelectrode layer 10. The OLED is thus also divided into a matrix of lightemitting picture elements 90.

[0044] Several OLEDs embodying the present invention may be fabricatedon a common substrate 10 and combined to produce larger area, higherresolution display panel. Electrically conductive paths may be providedin the substrate, or on the back face thereof, to facilitate theinterconnection of addressing and synchronization circuitry of adjacentOLEDs in the display panel. Because the OLEDs are fabricated on a commonsubstrate during the same deposition process, the characteristics ofeach OLED is uniform. Additionally, problems with aligning of the OLEDsrelative to each other are avoided.

[0045] In the embodiments of the present invention hereinbeforedescribed, the conductive layer 70 is partitioned into an array ofstrips running in a direction parallel to the strips of one of the first20 and second 40 electrode layers. However, it will be appreciated that,in other embodiments of the present invention, the conductive layer 70may be partitioned in both the direction of the strips of the firstelectrode layer 20 and the direction of the strips of the secondelectrode layer 40, thereby producing an array of conductive pads eachcorresponding to a different picture element 90 of the display and eachconnected to underlying strip of one of the first 20 and second 40electrode layers.

1. An organic light emitting device having a layer structure comprising:a first electrode layer (20); a second electrode layer (40) parallel tothe first electrode layer (20); an electrically conductive and lighttransmissive layer (70) parallel to the second electrode layer; anelectrically insulating layer (30) disposed between the first and secondelectrode layers; a layer of organic material (50) disposed between thesecond electrode layer and the conductive layer; an aperture (60) in theorganic layer providing an electrical connection path between theconductive layer and one of the first and second electrode layers.
 2. Adevice as claimed in claim 1, wherein the first electrode layer, secondelectrode layer, the insulating layer, and the conductive layer eachcomprise an array of parallel strips, the strip of the first electrodelayer extending orthogonal to the strips of the second electrode layer.3. A device as claimed in claim 2, wherein the strips of the insulatinglayer and the conductive layer extend orthogonal to the strips of thefirst electrode layer.
 4. A device as claimed in claim 2, wherein thestrips of the insulating layer and the conductive layer extendorthogonal to the strips of the second electrode layer.
 5. A device asclaimed in any of claims 2 to 4, comprising a plurality of apertures inthe organic layer each communicating with one of the first and secondelectrode layers.
 6. A device as claimed in claim 5, wherein eachaperture is located at a different intersection of a strip of the firstelectrode layer and a strip of the second electrode layer.
 7. A deviceas claimed in claim 5, wherein each aperture extends in a directionparallel to the strips of the second electrode layer.
 8. A device asclaimed in claim 5, wherein each aperture extends in a directionparallel to the strips of the first electrode layer.
 9. A device asclaimed in claimed in claim 3 wherein the strips of the conductive layerare electrically connected to corresponding strips of the secondelectrode layer.
 10. A device as claimed in claim 4 wherein the stripsof the conductive layer are electrically connected to correspondingstrips of the first electrode layer.
 11. A device as claimed in claim 1,wherein the layer structure is disposed on a substrate with the firstelectrode layer adjacent the substrate.
 12. A method for fabricating anorganic light emitting device, the method comprising: depositing a firstelectrode layer (20) on a substrate (10); depositing an electricallyinsulating layer (30) on the first electrode layer; depositing a secondelectrode layer (40) on the insulating layer; depositing an organiclayer (50) on the second electrode layer; forming an aperture (60) inthe organic layer; depositing a light transmissive electricallyconductive layer (70) on the organic layer; and forming an electricalconnection between the conductive layer and one of the first and secondelectrode layers via the aperture.